Hi, I can understand your concern for lump inside buttock crack. It appears the you have developed secondary infection on the butt crack area. You must see a doctor and preferably a surgeon to rule out any abscess at the area. For the time being period you to apply plain antibacterial cream such as fusidic acid or mupirocin (latest is retapamulin) and to take pain killer tablet by mouth for reducing the intensity of pain and redness. The only precaution you must follow is not to touch, pinch pop or squeeze any of them other wise it can get infected and can cause complications. Take care.